The disclosed invention is directed to noise generating circuitry, and is more particularly directed to a pseudorandom noise generator which produces pseudorandom noise by digital frequency modulation and is switchable for operation in different modes.
Pseudorandom noise generators are utilized in various applications such as system testing, secure communications, and electronic signal jamming. Depending on the application, certain characteristics of the output noise signal may be desirable. For example, a relatively narrow band output having a flat in-band spectrum and a high degree of spectral containment may be advantageous for jamming an individual victim receiver having a center frequency and bandwidth that are known approximately. As another example, a relatively wide band output having a flat in-band spectrum and a high degree of spectral containment may be advantageous for jamming a class of victim receivers which are known to be operating within a relatively wide bandwidth. In both examples, the high degree of spectral containment avoids jamming signals in other frequency ranges where jamming is not desired.
Disadvantages of known pseudorandom noise generators include the limitation of operating in only one mode. For example, a noise generator that provides a flat output for a low FM modulation index would generally be incapable of providing a flat output for a high FM modulation index. Another disadvantage of known pseudorandom noise generators is the use of complex analog circuitry which is subject to drift due to aging as well as changes in environmental conditions.